Error when add Gdata to project

I add Gdata to my project and set other C Flags:

Debug : -DDEBUG=1
Other Linker Flags : -lxml2 -ObjC
C Language Dialect:  C99 [-sd=c99]

But it show error in开发者_运维技巧 GDataServiceBase:

 "Duplicate interface declaration for class GMHTTPUploadFetcher".

What should I do to fix it ???